Oligonucleotides are substances comprised of a few nucleotides (DNA or RNA building blocks) whose nucleotide sequence consists in general of approx. 10-100 nucleotide units. Oligonucleotides are known as primers, for example, which are used in the polymerase chain reaction (PCR). Antisense oligonucleotides are oligonucleotides which have a base sequence that is complimentary to a cellular, viral or synthetic RNA or DNA and which can bind them by Watson-Crick base pairing. Such molecules are often directed against functional mRNAs. Due to the specific binding to the mRNA, ultimately the formation of the respective protein which is encoded by this mRNA is prevented by blockade of translation.
Antisense molecules may belong to various molecular classes to which antisense DNA (asDNA), “small inhibitory” RNA (siRNA), ribozymes and DNAzymes also belong. The last two groups of molecules are characterized by an inherent catalytic activity, which may lead to direct cleavage of the bound target RNA among other things.
As an example, but not exclusively, the DNAzymes of DE 103 46 487.5 are disclosed as examples of DNAzymes for producing an agent against inflammatory diseases.
It is known in general that oligonucleotides are very sensitive to naturally occurring or recombinant nucleases. Nucleases are a group of ubiquitous enzymes which usually act as hydrolases at ester linkages and catalyze the degradation of oligonucleotides. Those skilled in the art are familiar with nucleases as DNAses or RNAses.
The sensitivity of oligonucleotides to nucleases is problematical in medical use of oligonucleotides in particular. In comparison with traditional drugs, oligonucleotides can be degraded rapidly by DNAses and RNAses, which leads to a short half-life and thus to a lower bioavailability in the target cells.
In order for oligonucleotides to also be usable medicinally (in particular therapeutically), they must be protected effectively from the nucleases. To do so, great efforts are being made throughout the world with various technical approaches to modify the structure of oligonucleotides by chemical modifications, for example, in order to increase their stability or to develop drug carrier systems, i.e., so-called drug delivery systems. These drug delivery systems include, for example, liposomes, nanoparticles, viral shell capsids and protamine oligonucleotide particles.
Many of these drug delivery systems have disadvantages; for example, they do not provide adequate protection from degradation by nucleases, they have poor uptake into the target cells and tissue or they retain toxic or problematical constituents, which have a negative effect on the efficacy of the oligonucleotides. For topical application in particular, there is not currently a suitable preparation with which oligonucleotides such as DNAzymes can be formulated and administered as agents against inflammatory diseases because the formulations are not adequately protected against bacteria, fungi and nucleases. Successful use of oligonucleotides in dermatology has so far been prevented by this lack of options for protection.